There are insufficient published data on the potential health effects of dental amalgam
specifically to support or refute the diverse variety of health effects attributed to it.
Numerous studies constantly report effects on the central nervous system (CNS) in persons
occupationally exposed to Hg. Virtually all studies failed to detect a threshold for the
effects CNS measured. A tolerable daily intake (TDI) of 0.014 ug Hg/kg body weight/day was
proposed for mercury vapour, the principal form of mercury to which bearers of amalgam
fillings are exposed. This TDI was based on a published account of sub-clinical (i.e. not
resulting in overt symptoms or medical care) CNS effects in occupationally exposed men,
expressed as a slight tremor of the forearm. An uncertainty factor of 100 was applied to
these data, to derive a reference dose (TDI) which should, in all probability, prevent the
occurrence of CNS effects in non-occupationally- exposed individuals bearing amalgam
fillings.

The number of
amalgam-filled teeth, for each age group, estimated to cause exposure equivalent to the
TDI were: 1 filling in toddlers; 1 filling in children; 3 fillings in teens; and 4
fillings in adults and seniors. It was recognized that filling size and location (occlusal
versus lingual or buccal) may also contribute to exposure. However, data suggest that no
improvement in prediction of exposure is offered by any particular measure of amalgam
load. Therefore, the estimates of exposure derived from the number of filled teeth were
considered as reliable as those that might be based on size and position of amalgam
fillings, were such data available for the Canadian population.

Effects caused by allergic hypersensitivity to amalgam or mercury, including possible
auto- immune reactions, can not be adequately addressed by any proposed tolerable daily
intake. Individuals suspecting possible allergic or auto-immune reactions should avoid the
use of amalgam selecting suitable alternate materials in consultation with dental care
(and possibly health care) professionals.

Preface This report has been prepared in response to concerns that exposure to mercury
from dental amalgam may adversely impact on health. Recent reviews (USDHHS 1993, Swedish
National Board of Health, 1994) have concluded that there is no evidence to suggest that
dental amalgam, specifically, is injurious to health. However, the data base relating
health impacts in humans or animals to amalgam specifically is small and weak. This
suggests that indirect evidence relating mercury vapour exposure (the predominant form of
mercury released by dental amalgam) to human health effects (for which a large data base
exists) is a necessary basis for an evaluation of the possible health risks of dental
amalgam. In the reports previously mentioned, exposure to mercury arising from amalgam was
not adequately quantified, and a level of mercury vapour exposure which is, in all
probability, tolerable to the vast majority of persons bearing amalgam fillings, was not
defined. This report attempts to address these previous deficiencies.

This report is not exhaustive. Recent reviews on mercury (WHO 1990, 1991; IARC 1993;
ATSDR 1994) adequately review many aspects of mercury toxicity and exposure. Instead, this
report focuses on studies which report on health effects in dental care practitioners and
other occupational groups exposed to relatively low levels of mercury. This report also
examines recent research which hypothesizes a link between mercury exposure, and thereby
dental amalgam, and Alzheimers' Disease. This report concentrates on effects associated
with long term mercury vapour exposure (via inhalation) in humans. Other reviews (WHO
1990, 1991; IARC 1993; ATSDR 1994) examined acute and sub-chronic exposure in animals, and
all aspects of the toxicology of exposure to other forms of mercury via other routes of
exposure (ingestion, dermal absorption), in extensive and adequate detail such that this
is not repeated here.

Any medical or dental material, such as amalgam, will have associated with it some
degree of health risk. The purpose of this report is to attempt some determination of what
that risk is (i.e. what effect(s) it may cause), how significant it is (i.e. what level of
exposure should be free from effect), and what proportion of the population might be at
some degree of risk (i.e. how many exceed the level considered to be free from effect)